1. Field of the Invention
The present invention relates to a quantum interference device utilizing an interference phenomenon of electrons, and more particularly to a quantum interference transistor using a phase difference of electronic waves caused by a corrugated or periodic length structure of a gate capable of controlling a current amount flowing between a source and a drain thereof.
2. Description of the Prior Art
Wave nature of electron means that electrons are moved like a wave. Particularly, interference of electron means that, when two electronic waves passing through different paths meet again at the same position to add the waves to each other, the intensity of the resultant wave added thus is changed dependent upon a difference between the two different paths. In detail, it means that electron has a phase as a wave, and, if electrons having a different phase are moved in the same direction, the elections are interfered with one another, thereby causing totally flowing intensity of electrons, i.e. a current intensity to be changed.
These phenomena can be described by a quantum mechanics, and a transistor utilizing these phenomena is called "a quantum interference transistor".
This quantum interference transistor has the same transistor functions as a conventional semiconductor transistor, in which phases of electrons in channel thereof are, however, adjusted by a gate voltage, thereby allowing a drain current thereof to be controlled. Also, it has an operation characteristics of a high speed because of utilizing a ballistic movement.
In this quantum interference transistor, however, since the interference occurring in a solid state vanishes away by an inelastic collision of electrons and physical and material factors, to reduce such an inelastic collision is required so as to obtain operation of a transistor capable of being performed by a quantum dynamic interference, or to reduce the size of such a quantum interference transistor is required in order that electrons are interfered with one another prior to inelastic collision. The physical factor indicates phonon or the like and the material one does impurities, grain boundary or the like.
With the progress of a technique for growing crystal material of a high purity such as molecular beam epitaxy(MBE), metal organic chemical vapor deposition or the like, factors serving as inelastic collision in a thin film can be largely lowered. It also is possible to form a fine pattern using electron beam lithography progresses. Therefore, several types of quantum interference devices utilizing interference of electron have developed in recent years, typical one of which is a quantum interference transistor having a parallel-gate structure and is disclosed in Applied Physics Letters by D. R. Allee, etc. "Engineering lateral quantum interference devices using electron beam lithography and molecular beam epitaxy", pp 2015-2019 in 1989 American Journal of Vacuum Science & Technology.
FIG. 4 shows the construction of the disclosed quantum interference device having a parallel-gate structure. With reference to FIG. 4, the device is fabricated on a semi-insulating substrate with MBE(molecular beam epitaxy) layers grown at 580.degree. C. In detail, a GaAs layer having 40 nm in thickness is first grown followed by eight periods of an AlGaAs/GaAs superlattice. A buffer layer having 500 nm in thickness is then grown, followed by an undoped AlGaAs spacer layer having 2.5 nm in thickness, an AlGaAs layer doped with Si at 2.times.10.sup.18 cm.sup.-3, and finally an n.sup.+ GaAs cap layer. The sheet resistance for this wafer was 250 .OMEGA./sq. The thicker spacer layer increases the electron mobility in the heterojunction interface by reducing the Coulombic scattering. The cap layer also is so thin that the gate electrodes can be places directly on top avoiding the wide gate recess and simplifying the fabrication sequence.
However, in the prior art quantum interference transistor, since two gate electrodes are formed in parallel on the AlGaAs layer and all a source, a drain, and an electron path between them are composed of a two dimensional electron gas, such a quantum interference transistor uses the resonant tunneling effect and/or multiple reflection effect of the electron wave. Further, a high gate voltage is required therein to form a well-shaped potential well or barrier. As compared the quantum interference device to a semiconductor device having the same size as the interference device, the interference device has a number of channels and interference of electron is seriously lowered due to averaging of the number of channels. It is therefore difficult to use commonly.